A natural hip joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural hip joint with a prosthetic hip.
Various partial or complete replacements of the hip joint have been proposed and used since the early 1900's. Most of the procedures or methods involved material problems that led to joint loosening and consequential failure.
One widely used total hip replacement removes the femoral head and inserts a stem into the upper end of the femur, where it is fixed either by cement or by bone growth into a porous coating. A small metal ball, replacing the patient's femoral ball, is affixed to the stem. This technique requires massive bone removal and results in extreme loading of force in a leveraging action from the top of the femoral ball to a lower part of the stem. Over a few years, force applied by vigorous and mostly younger patients can cause the stem to loosen, resulting in failure, pain and need for extensive and expensive revisions. Additionally, such hips that use large femoral stems with metal on plastic articulations have had problems with dislocation due to small head sizes, as well as wear of the polyethylene acetabular components that have resulted in relatively rapid failures.
This need has led to the development of metal on metal femoral resurfacing components that require only that a portion of the femur head be resected or resurfaced, rather than the entire femur head. An early example of such an operation was developed by Derek McMinn, M.D. and Ronan Treacy, M.D. in Birmingham, England in the early 1990s.
One of the significant challenges of more general adoption of hip resurfacing is the accurate positioning of the femoral cap and its alignment with respect to the resurfaced femoral head, as well as the complementary alignment and positioning of the concave, hemispherical acetabular insert piece with which the femoral cap cooperates.
One of the major issues with adoption of this procedure in the United States over the past 6 or 7 years has been extremely difficult achieving appropriate component positioning. See Nunley et al., CORR 2010, Berend et. al JBJS 2011. (hereby incorporated herein by reference).
Accurate and reproducible component positioning is very challenging because the constituent joint bones are very irregularly shaped, and do not lend themselves to easy measurement in all of the dimensions necessary to resurface and reintroduce the bones into a cooperative, jointed disposition. After the dimensions and orientation of the femur and pelvic joint portions are approximated, the dimensions must then be changed by the reaming process in preparation for the resurfacing operation. To complete the operation, the correctly sized synthetic components must be installed to best fit the originally approximated femoral and pelvic dimensions.
Further complicating this process is that the surgeon must be able to operate under time constraints while performing the approximation and resurfacing procedures while the constituent bones are removed from their normal position, and freed from their surrounding soft tissue.
Various methods have been tried for this including computer navigation with very expensive computer navigation technology from companies such as Brain Lab. Other methods involve the use of physical devices such as sizing template devices.
Notwithstanding attempts by others to improve upon the required measurement and placement processes involved in hip resurfacing operations, the literature currently reflects a learning curve of nearly 100 to 150 cases for surgeons to gain adequate component positioning experience to be proficient. Several papers relate that even experienced hip surgeons will require at least 50 to 75 cases to achieve adequate component positioning with this Birmingham hip surfacing operation. See Nunley et al., CORR 2010. Such long learning curves extend the period during which there is a risk of less than optimal placement and installation, often requiring additional surgery to ultimately obtain a satisfactory result.
Accordingly, there remains a need for an accurate, inexpensive and reproducible method for the placement of hip resurfacing components that allows a surgeon to relatively quickly become highly proficient in the placement, sizing and installation of these components in hip arthroplasty surgery.